The present invention relates to an antidetection by radar device for a flattened superstructure of a ship.
It is known that the weaponry of a combat ship, in addition or instead of the usual guns and torpedos, comprises batteries of anti-ship missiles or of anti-aircraft missiles. These missiles and their launch means can be arranged as a superstructure on the deck of the ship. However, for obvious reasons of detectability by radar, it is preferable for said batteries of missles to be disposed as far as possible inside said ship.
In this case, said missiles can be disposed in vertical shafts disposed under the deck of said ship and occluded at their upper part by swiveling doors which, in the closed positionxe2x80x94that is to say when the batteries are idle outside a firing sequencexe2x80x94project slightly with respect to said deck.
When idle, the superstructure of said batteries of missiles therefore comprises said doors in the closed position. It may comprise, moreover, ducts for discharging the combustion gases from the motors of the missiles. In all cases, it is very flattened on the deck, jutting out from the latter by only a small amount. Therefore, the overall radar signature of the ship results mainly from its other superstructures, such as hull, bridge, gangway, masts, antennas, etc.
However, although relatively weak, the radar signature of the superstructure of such a battery of missiles when idle, partially enclosed under the deck, unfavorably influences the overall radar signature of the ship.
The object of the present invention is therefore to render the upper part of the superstructure of such batteries of missiles when idle stealthy, so that the overall radar signature of the ship is not affected thereby.
To this end, according to the invention, the device enabling a flattened superstructure carried by the deck of a ship to be rendered insusceptible to electro-magnetic waves, in particular the superstructure of an idle battery of missiles onboard a ship and said missiles of which are contained in vertical shafts disposed partially under the deck of said ship and occluded at their upper part by swiveling doors which, in the closed position, constitute said superstructure at least in part, is noteworthy in that it comprises:
at least on each of the port and starboard sides of said superstructure at least one inclined plane screen able to reflect an incident beam of electromagnetic waves in a different direction from that of said incident beam, said screens projecting with respect to said deck by a height greater than that of said superstructure and the inclination of said screens being such that they get closer to said superstructure as they get further from said deck; and
a net, reflecting the electromagnetic waves and stretched above said superstructure.
Thus, should a detection radar, disposed laterally with respect to said ship, dispatch an incident beam to said superstructure, it cannot receive the corresponding reflected beam, should said incident beam strike one of said plane screens or said protective net.
It will be noted that, by virtue of the presence of said protective net stretched above the superstructure, the height of said screens may be relatively small. Specifically, the incident radar beams passing above said screens and striking said net are also reflected in a different direction.
Preferably, said protective net is stretched between the free edges, away from said deck, of said inclined plane screens, so that the height of said net above the deck is equal to that of said inclined plane screens.
Thus, said inclined plane screens and said net form an antiradar protective enclosure enveloping said superstructure while rendering it particularly insusceptible.
To further increase this protective effect by envelopment, it is advantageous for the device in accordance with the present invention to comprise, in addition to the port and starboard inclined plane screens, additional similar inclined plane screens forming, with said port and starboard screens a polyhedron surrounding said superstructure, said protective net being stretched between the free edges of all said inclined plane screens.
In an advantageous embodiment of this type, said device comprises four inclined plane screensxe2x80x94including a port screen and a starboard screenxe2x80x94forming a frusto-pyramidal tetrahedron surrounding said superstructure.
Additionally, to prevent such antidetection protection from being an obstacle to the firing of the missiles, matters are contrived such that said height of the inclined plane screens and of said net is less than the length of the swiveling occluding doors and that said protective net can be ripped by each of said doors passing from the closed position to the open position. Thus, simply by opening the doors, the net is ripped and affords free passage opposite said shafts, so that the missiles can be fired instantaneously.
It will be noted that said net must, on the one hand, be able to be easily torn by the doors of the shafts when they open, but, on the other hand, be strong enough to withstand wind and heavy seas. It has been found that it is possible to satisfy these contradictory requirements by making said net with steel wires, the diameter of which is at most equal to 0.4 cm.
It is known, additionally, that detection radars emit beams of electromagnetic waves whose frequency lies between 2 and 18 GHz. It follows that, in order for said net to be able to reflect these electromagnetic waves, the largest dimension of its cells must be at most equal to 0.8 cm. Preferably, a net having square cells with sides most equal to 0.8 cm is chosen.
Additionally, to allow for the roll of the ship, as will be seen hereinbelow, the angle of inclination of said inclined plane screens with respect to the deck of the ship is chosen at most equal to 60xc2x0.